a) Field of the Invention
The present invention relates to vector control apparatus and method for controlling torque and speed of an induction motor through a vector control type inverter in which a magnetic flux observer of a full order is expressed in a state equation and has a plurality of coefficients expressed in circuit constants in a T-I type equivalent circuit to the induction motor.
b) Description of the Related Art
There are some kinds of vector control methods for an induction motor. There is a certain kind of vector control method for the induction motor in which a secondary magnetic flux of the induction motor is estimated using a flux observer and the induction motor is controlled on the basis of the estimated magnetic flux.
In addition, Japanese technical papers describing the application of the full order magnetic flux observer so as to add a compensation for a temperature variation of the secondary resistance of the induction motor and/or to achieve a speed control of the induction motor without use of a speed sensor.
That is to say, there are four published papers listed below:
1) a first Literature (Literature 1); "Adaptive Flux Observer of Induction Motor and its Stability" in T.IEE Japan Volume 111-D, No. 3 published on Mar. 3, 1991 and authored by Hisao Kubota and Kouki Matuse. PA1 2) a second Literature (Literature 2); "Performance of a Torque Control for Induction Motor Using State Observer" published on 1987 in National Meeting of Industrial Application Department on Japan Electrical Society and authored by Hideki Hashimoto, Yukou Ohno, Seiji Kondo, and Fumio Harashima. PA1 3) a third literature (Literature 3); "Direct Field Oriented Control of Induction Motor Without Speed Sensors using Adaptive Flux Observer" published on November of 1991 in a paper D of a Japan Electrical Engineering Society, Volume 111, No. 11 and authored by Hisao Kubota, Masanori Ozaki, and Kouki Matsuse. PA1 4) a fourth literature (Literature 4); "Hyperstability of the Full Order Adaptive Observer for Vector Controlled-Induction Motor Drive Without Speed Sensor" in a paper D of the Japan Electric Engineering Society published on January 1992, Volume 112, No. 11 and authored by Gung Yang and Tung-Hai Chin. PA1 R.sub.1 : Primary Voltage; PA1 R.sub.2 : Secondary Resistance; PA1 L.sub.1 : Primary Inductance; PA1 L.sub.2 : Secondary Resistance; and PA1 M: Mutual (Exciting) Inductance in a T type equivalent circuit to the induction motor;
Equations concerned with the full order magnetic flux observer are known from the above-listed literatures 1 and 2.
The literature 1 recites that the observer is constituted by the equations in a time-continuous system to which a numerical value integration such as an Euler method is applied.
On the other hand, the literature 2 recites that the observer is constituted by equations in a time-discrete system using a time-discrete model to reduce computation errors.
A general concept on the equation in the time-continuous system recited in the literature 1 will briefly be described below.
A state equation on stator coordinates of the induction motor is given by an equation (1) in TABLE 1.
In the TABLE 1, i.sub.1 denotes a primary current of the induction motor, v.sub.1 denotes a primary voltage, and .lambda..sub.1 denotes a secondary magnetic flux.
Furthermore, TABLE 2 shows respective coefficients (2-1) through (2-11) recited in the equation (1).
In the equation (1), the current, voltage, and magnetic constants are two-axis components but are expressed in terms of vectors to simplify the expressions of equation. Actually, the primary current, the primary voltage, and secondary magnetic flux mean two-axis components of .alpha.-.beta..
That is to say, the primary current, the primary voltage, and the secondary magnetic flux are expressed in three equations (3) in TABLE 3.
Constants (circuit constants) in the induction motor are represented as follows:
The magnetic flux observer of the full order recited in the literature 1 is expressed in the case where a pole arrangement of the observer is set to be k times as large as the pole arrangement hat the induction motor inherently has.
On the other hand, the magnetic flux observer provided in the vector control method can also be constituted by an equation (4) in TABLE 4. An estimation variable is represented by a superscript of .
In addition, feedback gains of the observer are expressed in equations (5-1), (5-2), (5-3), (5-4), and (5-5) in TABLE 5.
Utilizing the magnetic flux observer of the full order, induction motor drives without a rotor speed sensor such as a rotary encoder has been proposed in the literatures 3 and 4. In each of the literatures 3 and 4, in order to estimate the rotor speed, an adaptive control for the rotor speed has been carried out using the following speed estimation equations.
That is to say, error components between a model current and an actual current such as an excitation current or a torque current are defined in equations (6-1) and (6-2) in TABLE 6.
It is noted that the model current is a current flowing through a Model Reference Adaptive System (MRAS) recited in the literature 4 and a superscript of denotes an estimated value in the MRAS side.
Next, the rotor speed .omega.r is estimated from an equation (7) in TABLE 7 using the magnetic flux and error current components.